JPH05258889A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To prevent a discharge flame failure liable to occur when the dimming level is deepened, reduce the filament current, and suppress the shortening of a life. CONSTITUTION:A lighting device is provided with a rectifying circuit 2 rectifying an AC power source 1, a boosting circuit 3 boosting the output voltage of the rectifying circuit 2, an inverter circuit 4 converting the boost voltage of the boosting circuit 3 into the high-frequency voltage proportional to the boost voltage, a serial resonance circuit including an inductance 7 and a capacitor 8, and a preheating type discharge lamp 9 connected in parallel with the capacitor 8 and preheated by the current of the capacitor 8. An oscillation frequency control circuit 5 is interlocked with a boost voltage control circuit 6, and the whole of them forms one kind of a dimming circuit. The control characteristic of the dimming circuit including the oscillation frequency control circuit 5 and the boost voltage control circuit 6 is selected to reduce the boost voltage of the boosting circuit 3 and increase the oscillation frequency of the inverter circuit 4 in response to the deepening action of the dimming level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to dimming of a discharge lamp lighting device having a booster circuit and an inverter circuit.

[0002]

2. Description of the Related Art A conventional device shown in FIG. 6 includes a rectifier circuit 2 for rectifying an AC power source 1, an inverter circuit 4 for converting a rectified voltage into a high frequency voltage, and a series resonance circuit including an inductance 7 and a capacitor 8. A discharge lamp 9 and an oscillation frequency control circuit 5 that controls the oscillation frequency of the inverter circuit 4. In the apparatus shown in FIG. 6, the oscillation frequency control circuit 5 is appropriately operated to increase the oscillation frequency of the inverter circuit 4 for dimming. When the oscillation frequency is increased, the reactance value of the inductance 7 increases and the tube current of the discharge lamp 9 decreases. The conventional device shown in FIG. 7 has the same AC power supply 1 and rectifier circuit 2 as in FIG. 6, a booster circuit 3 for boosting the output voltage of the rectifier circuit 2, and a boosted voltage of the booster circuit 3 converted into a high-frequency voltage proportional to the voltage. An inverter circuit 4 for performing a series resonance circuit including an inductance 7 and a capacitor 8;
It comprises a discharge lamp 9 and a boost voltage control circuit 6 for controlling the boost voltage of the boost circuit 3. In the device of FIG. 7, the boost voltage control circuit 6 is appropriately operated to lower the boost voltage 4 applied to the inverter circuit 4 to perform dimming.

[0003]

In the conventional apparatus shown in FIG. 6, the oscillation frequency of the inverter circuit 4 during dimming must be increased to about 2-3 times that during full light lighting. Therefore, the filament current of the discharge lamp 9 passing through the capacitor 8 increases, and the life characteristic of the discharge lamp 9 during dimming is impaired. On the other hand, in the device of FIG. 7, the boosted voltage of the booster circuit 3 during dimming must be reduced to half or less than that during full-light lighting. Therefore, the discharge sustaining voltage of the discharge lamp 9 cannot be secured, and the discharge lamp 9 may go out. As described above, in the conventional device, when the dimming degree is deepened, there arises a problem that the life is shortened due to an increase in the filament current, or the lamp is extinguished due to insufficient discharge sustaining voltage. An object of the present invention is to solve the problems of shortening the life and disappearing in each of the above devices.

[0004]

SUMMARY OF THE INVENTION In the present invention, a dimming circuit is used which reduces the boosted voltage of the boosting circuit and raises the oscillation frequency of the inverter circuit in response to the operation of increasing the dimming degree. On the contrary, if the dimming degree is relaxed and it approaches the full light condition,
The boosted voltage of the booster circuit increases and the oscillation frequency of the inverter circuit decreases.

[0005]

When the boosted voltage by the booster circuit is lowered, it easily disappears, but this is compensated for by increasing the oscillation frequency, and the dimming degree is deepened. When the oscillation frequency of the inverter circuit increases, the filament current of the discharge lamp increases, but this increase is alleviated by the boosted voltage by the booster circuit, and the dimming degree is further deepened.

[0006]

EXAMPLE The example of FIG. 1 will be described below. This lighting device includes a rectifier circuit 2 that rectifies the AC power supply 1, a booster circuit 3 that boosts the output voltage of the rectifier circuit 2, and an inverter circuit 4 that converts the boosted voltage of the booster circuit 3 into a high-frequency voltage proportional to the voltage. , Inductance 7 and capacitor 8
And a series resonance circuit (7, 8) including a preheating type discharge lamp 9 connected in parallel with the capacitor 8 so as to be preheated by the current of the capacitor 8. An oscillation frequency control circuit 5 is attached to the inverter circuit 4. Reference numeral 6 denotes a boost voltage control circuit 6 attached to the boost circuit 3. The oscillation frequency control circuit 5 and the boost voltage control circuit 6 work together to form a kind of dimmer circuit as a whole. The control characteristics of the dimming circuit including the oscillation frequency control circuit 5 and the boost voltage control circuit 6 are such that the boost voltage of the boost circuit 3 is reduced as shown in FIG. Selected to increase frequency. The dimming method of the apparatus shown in FIG. 1 will be described with reference to FIG. When all the lights are lit, the boosted voltage of the booster circuit 3 is the highest V ₁ , and the oscillation frequency of the inverter circuit 4 at that time is the lowest f ₁ . Thus, V ₁
Is applied to the discharge lamp 9 via the inductance 7 having a low reactance value. Here, the boosted voltage control circuit 6 is manually operated to perform dimming. As a result, the boosted voltage increases from V ₁ to V ₂ . On the other hand, in conjunction with this, the oscillation frequency control circuit 5 operates to raise the oscillation frequency from f ₁ to f ₂ . When the dimming degree is further increased, the boosted voltage decreases from V ₂ to V ₃ and the oscillation frequency increases from f ₂ to f ₃ . Under this circumstance, the lowest voltage proportional to V ₃ is applied to the discharge lamp 9 via the inductance 7 having the highest reactance value corresponding to f ₃ , and the light is dimmed deeply. Further, the reactance value of the capacitor 8 is the lowest, and a slightly high current value is given to the electrodes of the discharge lamp 9. Under the condition of the boosted voltage V ₃ and the oscillation frequency f ₃ with deep dimming, the boosted voltage V ₃ alleviates the increase of the oscillation frequency, and the capacitor 8
Acts to relieve the current. Also, the oscillation frequency f
₃ acts to mitigate the decrease in boosted voltage and prevent discharge extinction under deep dimming conditions. In this way, by setting the boost voltage according to the dimming degree and adopting the control method in which the oscillation frequency is also changed according to the boost voltage, the boost voltage of the boost circuit 3 is reduced to half or less of that when all lights are turned on. In addition, the dimming degree can be deepened even if the oscillation frequency of the inverter circuit 4 is not set to about 3 or more at the time of full light lighting. As an example of the control characteristics of FIG. 2, the boosted voltage V ₁ at the time of all-light lighting is about 380 V, and the oscillation frequency f ₁ is about 55 k.
Hz. V ₂ shown is about 260V, f ₂ is about 72k
Hz, and the dimming degree at this time is about 50%. The illustrated V ₃ is about 200 V, and f ₃ is about 78 kHz. At this time, the dimming degree is about 20%, and no erasure occurs. Next, the circuit of FIG. 3, which is a more specific version of that of FIG. 1, will be described. The rectifiers 10, 11, 12, and 13 in FIG. 3 form a full-wave rectifier type rectifier circuit 2. A capacitor 14 smoothes the rectified output voltage. The inductance 15, the diode 16, the switching transistor 17, the drive circuit 18 thereof, and the capacitor 21 constitute a step-up chopper type booster circuit 3. The resistors 19 and 20 are attached to the boost control circuit 6. The inverter circuit 4 includes a pair of switching transistors 23 and 24 and a drive circuit 25 thereof. Capacitor 22 in series with series resonant circuit (7, 8)
Is for blocking direct current, and the capacitor 8
Can be ignored for. The inductance 15 is charged when the transistor 17 of FIG. 3 is conducting, and the electromagnetic energy of the inductance 15 is sent to the capacitor 21 via the diode 16 when it is not conducting. Thus, the boosted voltage is generated in the capacitor 21. The boosted voltage of the capacitor 21 is applied to the series resonance circuit (7, 8) via the transistors 23, 24 which are alternately conducting. Thus, a high frequency voltage having a peak value proportional to the boosted voltage is applied to the series resonant circuit (7, 8). The embodiment of FIG. 4 has the inductance 15 of FIG.
Insulating transformer 26 is used instead of
When 7 is non-conducting, its electromagnetic energy is isolated transformer 2
It is designed to be sent to the subsequent stage via the secondary winding of No. 6. In the embodiment shown in FIG. 5, the pair of transistors 23 and 2 is used.
4, a pair of capacitors 27 and 28 facing each other are added, and one end of a series resonance circuit (7, 8) including the discharge lamp 9 is connected to the midpoint thereof.

[0007]

According to the present invention, the increase in the oscillation frequency is mitigated by the boost voltage and the reduction in the boost voltage is mitigated by the oscillation frequency even under the condition of deep dimming. Therefore, it is possible to alleviate the extinction of the discharge lamp and alleviate the filament heating.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a discharge lamp lighting device according to the present invention.

FIG. 2 is a control characteristic diagram showing the relationship between the boosted voltage and the oscillation frequency.

FIG. 3 is a circuit diagram showing an embodiment of the present invention.

FIG. 4 is a circuit diagram showing another example of the booster circuit in the circuit of FIG.

FIG. 5 is a circuit diagram showing another example of the inverter circuit in the circuit of FIG.

FIG. 6 is a circuit diagram of a conventional device.

FIG. 7 is a circuit diagram of another conventional device.

[Explanation of symbols]

 1 ... AC power supply 2 ... Rectifier circuit 3 ... Booster circuit 4 ... Inverter circuit 5 ... Oscillation frequency control circuit 6 ... Boosted voltage control circuit 7 ... Inductance 8 ... Capacitor 9 ... Discharge lamp

Claims (1)

[Claims] 1. A rectifier circuit for rectifying an AC power supply, a booster circuit for boosting an output voltage of the rectifier circuit, an inverter circuit for converting the boosted voltage of the booster circuit into a high frequency voltage proportional to the voltage, an inductance and a capacitor. In a discharge lamp lighting device including a series resonance circuit including the preheating type discharge lamp connected in parallel with the capacitor so as to be preheated by the current of the capacitor, the boosting circuit of the booster circuit is operated in response to an operation of increasing the dimming degree. A discharge lamp lighting device comprising a dimming circuit that reduces a boosted voltage and increases an oscillation frequency of the inverter circuit.